[Issue]: Explain Stack Management

[bmulholland]

Type of issue

Missing information

What documentation page is affected

https://www.elastic.co/docs/deploy-manage/upgrade/prepare-to-upgrade/upgrade-assistant

What happened?

I'm trying to do an upgrade, and the docs strongly recommend running Upgrade Assistant. I'm trying to find that, and the docs just refer to "open Stack Management." Which doesn't exist anywhere in the many screens I can find...

There's also no docs anywhere that explain or show where I can expect to find this mythical "Stack Management"

Maybe I don't need this step? Maybe Stack Management isn't available on my plan? The docs should say that, especially when strongly recommending something.

Additional info

No response